1. Field of the Invention
This invention relates to an improved process for the recovery of hydrocarbon materials from hydrocarbon-bearing formations. More particularly, the invention relates to a process in which hydrocarbons, including asphaltic crudes, are recovered from a reservoir by contacting the formation with an aqueous alkaline flooding medium containing a solubilizing agent.
2. Description of the Prior Art
The production of petroleum products is usually accomplished by drilling into a hydrocarbon-bearing formation and utilizing one of the well-known recovery methods for the recovery of the hydrocarbons. However, it is recognized that these primary recovery techniques may recover only a minor portion of the petroleum products present in the formation particularly when applied to reservoirs of viscous crudes. Even the use of improved recovery practices involving heating, miscible flooding, water flooding and steam processing may still leave up to 70-80% of the original hydrocarbons in place.
Thus, many large reserves of petroleum fluids from which only small recoveries have been realized by present commercial recovery methods, are yet to reach a potential recovery approaching their estimated oil-in-place.
Water flooding is one of the more widely practiced secondary recovery methods. A successful water flood may result in recovery of 30-50% of the original hydrocarbons left in place. However, generally the application of water flooding to many crudes results in much lower recoveries.
The newer development in recovery methods for heavy crudes is the use of steam injection which has been applied in several modifications, including the "push-pull" technique and through-put methods, and has resulted in significant recoveries in some areas. Crude recovery by this process is enhanced through the beneficial effects of the drastic viscosity reduction that accompanies an increase in temperature. This reduction in viscosity facilitates the production of hydrocarbons since it improves their mobility, i.e., it increases their ability to flow.
However, the application of these secondary recovery techniques to depleted formations may leave major quantities of oil-in-place, since the crude is tightly bound to the sand particles of the formation, that is, the sorptive capacity of the sand for the crude is great. In addition, interfacial tension between the immiscible phases results in entrapping crude in the pores, thereby reducing recovery. Another disadvantage is the tendency of the aqueous drive fluid to finger, since its viscosity is considerably less than that of the crude, thereby reducing the efficiency of the processes.
Consequently, process modifications have been developed which may incorporate additives to lessen the above cited disadvantages and thereby improve the efficiency of these processes. For example, surface-active agents and miscible liquids are utilized to decrease the interfacial tension between the water and the reservoir crude, and thickeners have been developed to adjust viscosity so as to inhibit fingering.
The practiced methods for the injection of additives commonly consist of injection of a slug of additive, contained in a transporting medium, e.g. water, into the formation and then following this injection with a flood water to move the additive slug through the formation. In its ideal effect, the so-called slug moves through the formation as an additive bank, thereby imparting its beneficiating effects to the recovery process.
In many hydrocarbon-bearing formations it is common to find the oil sands to be preferentially wetted by oil. It is well known in the art to inject into these preferentially oil-wetted formations certain chemicals to reverse the wettability characteristics of the formation, thereby increasing the effectiveness of a water flood to remove the residual crude. For example, a dilute alkaline aqueous solution is known to increase the wetting characteristics of sand surfaces, and promote a leaching action and emulsification of the tarry materials. Those solutions have been used as slugs in conjunction with subsequent steam injection processes to force the emulsions thus formed through the formation to a production well.
Improved recoveries from heavy crudes or tar sands have been realized also by the use of dilute aqueous alkaline solutions containing an effective amount of non-ionic surfactant, whereby extraction is effected by the spontaneous emulsification when the aqueous liquid comes in contact with the tar in the sand.
However, some of the disadvantages of those additive recovery processes include the problem that the additive may be strongly absorbed in the surfaces of the sand formation, resulting in a large or excessive amount of additive being required. The costs involved of these additives, which may be relatively expensive, may become excessive early in the life of the recovery process necessitating its termination. Other disadvantages include the unfavorable viscosity ratio between the flooding medium and the crude.
It is known that the recovery of oil by injection of water or other fluids varies substantially from one formation to another and it is believed that the asphalt content of the hydrocarbons of some formations is at least a major factor responsible for this variation. A variety of known asphalt dispersants have been employed in flooding media on the theory that such materials would substantially improve hydrocarbon recovery in those instances where asphalt was present in the native hydrocarbon, however, the use of such materials has not been particularly effective, probably because of the limited solubility of such agents in the normally employed flooding fluids. There is a definite need in the art, therefore, for a recovery process employing asphalt dispersants with improved solubility characteristics.
One of the principal objects of this invention is to provide an improved process for increasing the ultimate recovery of hydrocarbon from a hydrocarbon-bearing formation.
Another object of this invention is to provide an efficient method for the recovery of hydrocarbon from a hydrocarbon-bearing formation in which an aqueous alkaline flooding medium containing as a solubilizing agent a watersoluble, oxyalkylated, nitrogen-containing aromatic compound is utilized.